• 한국전산유체공학회지
• /
• 제21권1호
• /
• pp.36-42
• /
• 2016

One of the obstacles on the grid generation for complex geometries with multi-block structured grids is the domain decomposition. In this paper, the domain decomposition for two-dimensional flow is studied using the flow characteristics. The potential flow equation with the source distribution on the panel surface is solved to extract the information of the flow. The current approach is applied to a two-dimensional cylinder and Bi-NACA0012 problems. The generated grids are applied to generic flow solvers and reasonable results are obtained. It can be concluded that the current methods is useful in the domain decomposition for the multi-block structured grid.

• 대한기계학회논문집B
• /
• 제29권6호
• /
• pp.671-686
• /
• 2005

The transient nature and complex geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. The velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method, and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for simulating slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are proposed for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• 대한수학회논문집
• /
• 제15권1호
• /
• pp.155-172
• /
• 2000

Mode interactions at Unstable fluid interfaces induced by a shock wave (Richtmyer-Meshkov Instability) are studied both analytically and numerically. The analytical approach is based on a potential flow model with source singularities in incompressible fluids of infinite density ratio. The potential flow model shows that a single bubble has a decaying growth rates at late time and an asymptotic constant radius. Bubble interactions, bubbles of different radii propagates with different velocities and the leading bubbles grow in size at the expense of their neighboring bubbles, are predicted by the potential flow model. This phenomenon is validated by full numerical simulations of the Richtmyer-Meshkov instability in compressible fluids for initial multi-frequency perturbations on the unstable interface.

• 대한기계학회논문집
• /
• 제5권4호
• /
• pp.354-361
• /
• 1981

This study aims to compare stress concentratior factors in a loaded elastic body of the infinite plate with pressure coefficients of a fluid in the potential flow. First in view of hydrodynamics, when a single elliptic cylinder in the form of a bluff body stands in the potential flow, the pressure distribution(doefficient, C$\_$p/around the elliptic cylicder which is changed according to the position(angular displacements)is theoretically analyzed and calulated; secondly, in view of theory of elasticity, when an eliptic hole which is made on a flat plate gets tension, the stress distribution(factor) around the elliptic hole which is changed according to the position(angular displacements )is theoretically(K$\_$t/) and experimentally (K$\_$e/) measured; and finally. The results are compard and examined.

• 한국환경과학회지
• /
• 제6권4호
• /
• pp.313-322
• /
• 1997

한국수영만에서 잔차류장의 운동 위치에너지의 계절변화를 연구하기 위하여 우리는 에너지의 수지를 계산하고 조석에너지와 비교했다. 위치에너지는 겨울과 봄철에 크며, 밀도성층이 형성된 여름과 초가을에 작게 나타났다. 잔차류의 운동에너지는 계절적인 변화를 보이고 있으며, 단위면 적당 잔차류의 평균 운동에너지는 6.4$\times$$10^{-4}ergs s^{-1}cm^{-}2$이다. 수영 만에서 잔차류장의 계절변동은 조석잔차류의 운동에너지가 밀도류나 취송류의 운동에너지보다 큰 11월을 제외하고는 밀도류가 지배하고 있다. 잔차류의 주성분인 조석잔차류, 취송류 및 밀도류의 운동에너지의 평균백분율은 잔차류의 운동에너지에 대하여 각각 29.1%, 3.4%, 67.5% 이다. 단위면적당 잔차류의 운동에너지, 위치에너지 및 조석에너지의 비는 각각 1.0 : 6.7$\times$$10^3$ : 8.2$\times$$10^4$ 이다.

• 한국산학기술학회논문지
• /
• 제21권10호
• /
• pp.415-420
• /
• 2020

군중 유동은 대도시의 철도 환승역, 터미널, 복합 다중 건물, 경기장 등에서 흔히 볼 수 있으며, 이러한 시설물에서의 이용객들의 원활한 흐름 뿐만아니라 안전 확보측면에서도 중요한 요소이다. 본 연구에서는 새로운 군중 유동 해석법을 개발하여 철도 환승 연결로 모델에 대하여 적용하였다. 해석법에서는 출구의 포텐셜 값을 가장 작은 값으로 입력하고, 주변 격자들의 포텐셜 값은 점진적으로 증가시켜서 전체적인 포텐셜 지도를 구성한다. 포텐셜 값이 큰 격자에서 작은 격자로 이동하는 방향 벡터를 구하여 이를 따르는 유적선을 구한다. 이 유적선이 여객 유동의 기본 경로가 된다. 해석 대상의 모든 모델에서, 보행자들은 처음 예측된 최단 거리 경로로 이동하지 않고, 시시각각의 상황에 따라 변경된 대체 경로를 이용하여 이동하였다. 양 방향의 보행자가 서로 마주치는 병목 구역에서도 진입 시차를 두어 분산시키면 보행이 훨씬 더 원활하게 되었다. 이상의 해석 결과로부터, 철도역의 하드웨어적 개량 공사를 하지 않고, 여객 유동 분석과 같은 소프트웨어적 해석으로도 혼잡 완화 방안을 찾을 수 있음을 보여준다.

• 대한기계학회논문집
• /
• 제3권4호
• /
• pp.181-184
• /
• 1979

Three-dimensional potential flow due to the translation of a sphere touching a rigid plane wall or a free wall is investigated by use of tangent sphere coordinates. Exact expressions for the velocity potential are derived in integral formes. Added mass and lift force on the sphere are also calculated.

• 대한기계학회논문집A
• /
• 제28권9호
• /
• pp.1320-1327
• /
• 2004

An efficient boundary-based technique is developed for addressing shape design sensitivity analysis in supercavitating flow problem. An analytical sensitivity formula in the form of a boundary integral is derived based on the continuum formulation for a general functional defined in potential flow problems. The formula, which is expressed in terms of the boundary solutions and shape variation vectors, can be conveniently used for gradient computation in a variety of shape design in potential flow problems. While the sensitivity can be calculated independent of the analysis means, such as the finite element method (FEM) or the boundary element method (BEM), the FEM is used for the analysis in this study because of its popularity and easy-to-use features. The advantage of using a boundary-based method is that the shape variation vectors are needed only on the boundary, not over the whole domain. The boundary shape variation vectors are conveniently computed by using finite perturbations of the shape geometry instead of complex analytical differentiation of the geometry functions. The supercavitating flow problem is chosen to illustrate the efficiency of the proposed methodology. Implementation issues for the sensitivity analysis and optimization procedure are also addressed in this flow problem.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1047-1052
• /
• 2004

An efficient boundary-based technique is developed for addressing shape design sensitivity analysis in supercavitating flow problem. An analytical sensitivity formula in the form of a boundary integral is derived based on the continuum formulation for a general functional defined in potential flow problems. The formula, which is expressed in terms of the boundary solutions and shape variation vectors, can be conveniently used for gradient computation in a variety of shape design in potential flow problems. While the sensitivity can be calculated independent of the analysis means, such as the finite element method (FEM) or the boundary element method (BEM), the FEM is used for the analysis in this study because of its popularity and easy-touse features. The advantage of using a boundary-based method is that the shape variation vectors are needed only on the boundary, not over the whole domain. The boundary shape variation vectors are conveniently computed by using finite perturbations of the shape geometry instead of complex analytical differentiation of the geometry functions. The supercavitating flow problem is chosen to illustrate the efficiency of the proposed methodology. Implementation issues for and optimization procedure are addressed in this flow problem.

• 대한기계학회논문집
• /
• 제19권12호
• /
• pp.3360-3371
• /
• 1995

Hydrodynamic characteristics of a stratified flow at a Y-junction were examined analytically. Gas is supplied through the main horizontal channel and liquid is introduced into the gas stream from the Y-shaped bottom branch. Analysis was performed with irrational flow and inviscid fluid assumptions. The Stokes' inverse transformation technique was adopted to convert the real x-y plane into the x-.psi. plane. The potential flow equation was solved numerically in the transformed (x-.psi.) plane and the interface profile, pressure distribution and the streamlines were obtained. The effects of the inlet conditions, injection angle and the gravity on the flow characteristics were also examined. To check the validity of the present method, the previous resultant the two-dimensional obtuse wedge flow was compared. The inverse transformation technique turned out to be also very useful to predict the hydrodynamic characteristics of a stratified flow with the pressure variation at a Y-shaped mixing junction.